1. Field of Invention
The present invention relates to a method and apparatus for automatically sensing the configuration of a surface area of an object, such as a portion of a hydraulic turbine runner located in a pit of a turbine generator and effecting a work function such as the repair of cavitation damage thereon, and more particularly to the use of a robotic system for the in-situ repair of such damage.
2. Description of Prior Art
The present invention originated by solving the problem of repairing hydraulic turbine runners in power stations which are often damaged by cavitation due to erosion. Such runners are often subjected to severe damage requiring extensive repair which is extremely costly due to the lengthy down time of the runner and because of the difficulty in effecting such repairs. The most economical way of repairing such turbines is to perform the work with the runner remaining in the turbine pit. The steps involved in the repair include air-arc gouging and/or grinding to remove unsound metal, followed by welding to fill the gouged-out areas. Finally, the weld-filled cavity must be ground to restore optimum blade profile. During these activities within the confined area of the turbine pit, workers are subjected to a number of hazards including fumes, noise, spatter, arc radiation, and flying particles of metal during grinding. Furthermore, limited access to damaged areas often requires the workers to operate in awkward and uncomfortable postures,
In order to reduce the hazards of such repairs the worker must use welding elements equipped with air filtration with a fresh air supply, and the provision of large fans to ventilate the turbine runner area. Nevertheless, this still remains a difficult environment in which to work, and there is potential health hazards due to poor ventilation and uncomfortable working conditions. All this adds to significant adverse effect on productivity, and may also influence the quality and integrity of the repair.
There is known a few mechanical systems in the prior art which are rail-mounted and which can transport a tool and displace this tool over a surface and at a speed which is adjustable by an operator. One type of such system utilizes a deformable rail that may be adjusted to the shape of a surface and usually along one or two axes which are straight and perpendicular to one another. If such a system is utilized to effect a work function on a complex surface, it is necessary that between each sweep or pass of the working element the operator intervenes to make an adjustment to the apparatus, such as the displacement of the rails, before the apparatus effects a second pass. Another system is known where an apparatus can sweep a surface without the intervention of an operator, but these surfaces must be of a constant shape, such as a cylinder. With such system the rail follows the profile of the cylinder with the robotic tool always maintained parallel to the surface. An example of such robotic apparatus is that utilized to deposit weld beads internally of a cylinder by means of a welding torch. However, the cylinder has a perfectly round surface and there is no need to adjust the apparatus.
In order to effect a work function on surfaces that are complex, one can consider utilizing an industrial robot which functions using the playback principle. When using this playback principle it is necessary to teach the robot, point by point, the trajectory of the working tool over the entire surface to be covered by the robot. This may represent thousands of points over a given surface, and the programming or teaching time becomes extremely long. This type of system is feasible when a robot is used to effect a repetitive work function, such as spot welding a specific frame or other type device. However, such system is not feasible for use in repairing objects, such as turbine runners, where each repair function has its own geometry. Also, such industrial robots are too large, heavy, and cumbersome to be attached to an object to effect a work function, in situ, in an area where space is restrained, such as in a pit of a turbine engine.